Closures for use with bottles and jars in the packaging of various consumer liquids, including cosmetics, vegetable oils, vinegar, drugs and household preparations of various kinds, are generally internally threaded for mating with a similar externally threaded bottle neck or a snap or lug closure. Such closures are commonly formed of plastic or metal and may have an insert or liner on the inside of the top of the cap to form a generally fluid-tight seal against the ends of the bottles to which they are applied. Recently, linerless closures have been introduced wherein an annular flange integral with the closure projects downwardly from the inside of the top of the cap. As the closure is screwed onto the bottle, the annular flange engages against the inner wall of the bottle neck and thereby forms a tight seal with the bottle neck.
In the molding of plastic or glass bottles and jars, the precision of forming the mouth of the container in a perfect circle is somewhat lacking, thereby presenting a mouth surface on the container of considerable unevenness, both in cross-section and circular configuration. Such nonuniformities or irregularities make it difficult to obtain a proper seal on every bottle with a linerless cap. Further, with thin-walled plastic containers, there is a tendency of the container mouth walls to collapse from the torque generated in screwing the closure on.
In an effort to solve the above-noted problem, U.S. Pat. No. 3,844,439 to Demers, et al. teaches the use of an inner annular sealing ring, an intermediate compression seal, and an outer annular sealing ring whereby the inner and outer sealing flanges are deflected over the inner and outer peripheral portions of the container mouth respectively. The central compression ring or flange provides additional sealing capability while limiting further travel of the closure. However, some bottle mouths are greatly out-of-round, and the dimensional variations in the mouth of such a bottle are of such a nature and extent as can cause the container mouth to lose physical contact with the flanges or flex them to such an extent as to lose the sealing engagement between the closure and the container.